In the paper converting and roll producing industry packaging machines are known for producing single or multiple packs of rolls of tissue paper, such as toilet paper, kitchen towels or the like. Some of these machines use, to wrap and package the rolls, sheets of plastic material, in particular polyethylene or the like. In these machines, a group of rolls, appropriately arranged in one or more rows and in one or more layers, are inserted into a sheet of plastic and subsequently moved forward by means of a conveyor through a folding station. In the folding station, the flaps projecting from both sides of the group of rolls are folded against the front surfaces of the rolls. At the exit of the folding station the pack thus obtained is made to pass through a sealing station which, by means of suitable heating systems, heats and seals together the folded flaps of the plastic sheet. Examples of machines of this type are disclosed in U.S. Pat. No. 6,067,780; EP-A-0995682; U.S. Pat. No. 7,789,219; EP-A-1067048; EP-A-1228966; US-A-20050229546. Examples of devices for sealing folded lateral flaps of the pack are described in WO-A-2004/024565 and in US-A-20040151481.
Machines of this type are commonly used to produce packs of multiple rolls, normally arranged in adjacent rows and if necessary in several superimposed layers.
In other prior art machines each roll is packaged individually, wrapping it in a sheet of plastic, or more commonly of paper, whose flaps projecting from the flat faces of the roll are folded and inserted into the axial hole of the tubular winding core around which the roll is formed. This packaging system typically goes by the name of “twist-and-tuck”, as the flap of the wrapping sheet projecting from each side of the roll is twisted, and then thrust inside the axial hole of the tubular winding core of the roll. Machines of this type are described, for example, in U.S. Pat. No. 4,651,500 and in EP-A-1518787. In particular, in the machine described in EP-A-1518787 the rolls are moved forward individually by means of a conveyor through a folding station. The flaps of the wrapping sheet, projecting from the two sides of the roll, beyond the front faces of said roll, are twisted around themselves, for example by means of a roto-translational movement between two folding profiles. Subsequently, punches moving parallel to the axial direction of the rolls and provided with a reciprocating movement orthogonally to the direction of feed of the rolls, penetrate the tubular core of each roll and insert the previously twisted lateral flaps of the wrapping sheet into the tubular core. The structure of the machine is complex and very bulky, in particular in the dimension parallel to the direction of feed of the rolls.